Chile has given nearly 57,000 18-year-olds one month to report for potential military duty, saying the government needs to fill gaps in its armed forces because a nationwide student protest movement has reduced the number of volunteers it usually gets.

Military service is obligatory in Chile, but there are usually enough volunteers to fill the ranks so that no one has to serve against their will.

So far this year, 14,127 men and women born in 1993 have signed up, and the armed forces deputy secretary, Alfonso Vargas, has said they need a bigger pool to choose from to fill 11,340 spots. That's why 56,793 more teenagers will need to report in a month for potential duty in 2012, he explained on the draft office's website.

Vargas blamed the student movement that has been campaigning for education reform since April for leading thousands of young people to boycott schools, and thus closing their doors to military recruiters.

General Gunther Siebert, who directs Chile's military draft, also blamed the student movement in an interview published in the El Mercurio newspaper, and said that 2.5 candidates are needed for every spot because many can't serve for physical or other reasons.

But Chile's military also had a shortage last year, before the movement began, and at that time it called up fewer than 39,000 for the draft.

To have 2.5 candidates for each spot, the military would need to call up only 14,223 more youngsters. Instead, so many more have been told to report that Chile could have more than six candidates for each position. The Associated Press asked Chile's national draft office in writing for an explanation, as requested by its spokesman, and did not immediately receive a response.

To find out whether they've been drafted, Chilean 18-year-olds must go to a military website and enter their national identification number. Many have been doing so and then commenting about it on social networks, where a popular tweet asks why Chile seems to value military service more than education by making it obligatory.

Unlike in some other countries, attending a university does not enable young Chileans to avoid the draft. The only exceptions are physical limitations, providing the primary income for a family, being married or expecting a child, being convicted of an "immoral" crime, or being the child of someone imprisoned or tortured by Chile's 1973-1990 dictatorship.